In situ pore pressures: What is their significance and how can they be reliably measured?

Strout, James Michael; Tjelta, Tor Inge

doi:10.1016/b978-0-08-044694-3.50027-5

Cited by 15 publications

(35 citation statements)

References 6 publications

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“…Perhaps the most significant difference in the mechanical behaviour of submarine vs terrestrial materials, is that elevated pore pressures may decline very slowly in submarine hillslopes relative to the rates in terrestrial settings (Leynaud et al, 2004;Strout and Tjelta, 2005;Sultan et al, 2008). This lower dissipation rate reflects factors including low permeability (fine grained) materials and permanently saturated sediments.…”

Section: Triggering Submarine Earthflow Movementmentioning

confidence: 95%

Terrestrial-style slow-moving earthflow kinematics in a submarine landslide complex

et al. 2009

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Section: Triggering Submarine Earthflow Movementmentioning

confidence: 95%

Terrestrial-style slow-moving earthflow kinematics in a submarine landslide complex

et al. 2009

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“…In tectonically active regions, such as accretionary prisms, overpressures have been cited as the driving force for large‐scale fluid flow leading to pore fluid chemical variations, and overpressures may mediate fault localization and earthquake slip. Technological advancements have increased our ability to measure overpressure, which has led to significant advances in our understanding of these systems, their dynamics, and the coupling of fluids and solids related to deformation and fluid flow [e.g., Strout and Tjelta , 2005; Flemings et al , 2008; Stigall and Dugan , 2010]. Based on the importance of overpressure in offshore soft sediments, where strengths are typically very low, accurate characterization of the pore pressure profile is essential.…”

Section: Introductionmentioning

confidence: 99%

Offshore sediment overpressures of passive margins: Mechanisms, measurement, and models

Dugan

Sheahan

2012

Reviews of Geophysics

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[1] Fluid pressure in excess of hydrostatic equilibrium, or overpressure, in offshore environments is a widespread phenomenon that contributes to the migration and storage of fluids, solutes, and energy and to the potential mechanical instability of these sediments. Overpressure exists in deep and shallow systems and is most likely to be found where low-permeability (<10 À16 m 2 ) layers have inhibited pore fluid escape or there have been large forcing mechanisms (e.g., rapid sedimentation, tectonic stressing, heating, and volume-creating reactions). The genesis and magnitude of overpressure can be controlled by physical processes (e.g., rapid sedimentation (>mm/yr), tectonic loading, and lateral fluid transfer) and thermal and chemical processes (e.g., aquathermal expansion, hydrocarbon generation, mineral diagenesis, and organic maturation). In systems where nearlithostatic overpressures are generated, potentially unstable sediments are created. Failures of these sediments can create large-scale natural disasters, generate fractures, and damage seafloor and subseafloor infrastructure. Detailed characterization of overpressured systems has been accomplished through geological and geotechnical analyses, including investigation of physical-mechanical properties (mainly porosity, consolidation state, and shear strength), inversion of geophysical data (e.g., compressional and/or shear velocities), measurement of in situ properties, and postevent analyses. Process-based models have been developed to explain the origin of overpressure in terms of rate of overpressure genesis. This allows identification of potentially unstable zones and assessment of the potential for failure. Future development in measurements and in coupling of models will lead to more accurate analysis and prediction of fluid pressure in offshore sediments, which in turn will facilitate better hazard analyses and will enable safer and more cost-effective offshore drilling practices and other offshore infrastructure development.Citation: Dugan, B., and T. C. Sheahan (2012), Offshore sediment overpressures of passive margins: Mechanisms, measurement, and models, Rev. Geophys., 50, RG3001,

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“…Estimated excess pore pressure from piezometers(Strout and Tjelta 2005) Excess pore pressure ratio in % of hydrostatic. Site locations are shown onFig.…”

mentioning

confidence: 99%

The role of sedimentation rate and permeability in the slope stability of the formerly glaciated Norwegian continental margin: the Storegga slide model

2007

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Despite the gently dipping slopes (ca 1°), large-scale submarine slope failures have occurred on the mid-Norwegian continental margin (Storegga, Sklinnadjupet, Traenadjupet), suggesting the presence of special conditions predisposing to failure in this formerly glaciated margin. With a volume estimated between 2,400 and 3,200 km 3 and an affected area of approximately 95,000 km 2 , the Storegga slide represents one of the largest and best-studied submarine slides of Holocene age known worldwide. Finite element modeling of slope failure indicates that a large (6.5< Ms<7.0) seismic triggering mechanism would not be sufficient to cause failure at more than 110 m below the seabed as observed for the slip planes at Storegga (northern sidewall). This implies that other factors (e.g., liquefaction, strain softening, gas charging, rapid burial) are needed to explain the occurrence of the Storegga slide with a deep surface of failure. In this paper, we discuss the importance of the compaction effect of rapidly accumulated sediments in the slide area. During compaction, sediment grains reorganize themselves, thereby, expelling pore water. Consequently, depending on sedimentation rate and permeability, excess pore pressures might result beneath less permeable sediments. Our modeling and cross-checking illustrate how excess pore pressure generation due to high sedimentation rate could explain the development of layers of weakness, and thus, how such a large slide might have been initiated in deep sediments. Using the highest sedimentation rate estimated in the area (36 and 27 m/kyr between 16.2 and 15 kyr BP), 1D modeling shows excess pore pressure values of around 200 kPa at a depth of 100 m below the seafloor 15 kyr BP and 60 kPa at a depth of 100 m at the time of the slide (8 kyr BP). Excess pore pressure apparently drastically reduced the resistance of the sediment (incomplete consolidation). In addition, 2D modeling shows that permeability anisotropies can significantly affect the lateral extent of excess pore pressure dissipation, affecting, that way, normally consolidated sediments far from the excess pore pressure initiation area.Landslides 4 • (2007) 309

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In situ pore pressures: What is their significance and how can they be reliably measured?

Cited by 15 publications

References 6 publications

Terrestrial-style slow-moving earthflow kinematics in a submarine landslide complex

Terrestrial-style slow-moving earthflow kinematics in a submarine landslide complex

Offshore sediment overpressures of passive margins: Mechanisms, measurement, and models

The role of sedimentation rate and permeability in the slope stability of the formerly glaciated Norwegian continental margin: the Storegga slide model

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